195/75R14, 205/75R14 and 215/65R15 were stock sizes back in the day (GNX used 245/50R16). To maintain speedometer accuracy, aim for a 25.7"-26.1" tire, but in the rear, go as big as will fit, but plan to fix your speedometer gears if you care to stay in the realm of posted speed limits.
8" rims typically fit with a 4.5" backspacing (ex: Corvette steel rally rim, correct me if I'm wrong). Section width up to 9.5" typically clears the rear frame rails and probably fits without rubbing up front (depending upon final choice of diameter, etc.)
I pulled data from several brand specification posted on Tire Rack, the actual numbers may vary slightly. I tend to be conservative, so my color coding is intended to guide you towards what is expected to fit without much modification. No warranty implied!
If you choose to use late-model Camaro rims, be aware that the bolt pattern is not precisely 5x4.75" (120.7mm), it's actually 120 mm. Since you have correct for the positive offset in late-model rims, EBay abides with a 1.5" to 2" thick wheel stud-type adapter 5x120 to 5x120.7. Not everyone is willing to use spacer/adapters.